Farmers must remain vigilant during the risk period for lungworm, writes Tommy Heffernan. In the last few weeks, the top query I have been receiving is in relation to cattle coughing. There are numerous reasons cattle can be coughing and it is extremely dangerous to make presumptions about a cause. What you need to do is carefully question the symptoms, the onset, the type of cough, discharges and dosing history. Most importantly, I find you need to examine them and do some diagnostics to find the exact cause of the cough. The number one issue I have seen is lungworm. However, I have seen lungworm with secondary viral pneumonias and some have been primary viral pneumonias also.
So the basis for this article is to raise awareness about lungworm control. The conditions have been perfect for lungworm larvae levels on pasture to be very high. Subsequently, we are seeing all groups of cattle of various ages being affected.
Vet, Tommy Heffernan
Life cycle
First, we must understand the life cycle of lungworm. When cattle eat the larvae, they are ingested and penetrate the intestine wall where they migrate to the lungs and develop into adult lungworm.
This adult lungworm produces eggs which are coughed up and then swallowed by the animal. This takes 24 to 28 days from initial ingestion. These eggs then hatch to early larval stage in the intestine and are passed out in the dung.
They then develop into the infective larval stage in the dung and then swim and are assisted by a fungus/rainfall to get on to the grass. Wet, mild and damp conditions greatly help this process. If conditions are right, this can occur in seven days.
They can survive over winter on pasture in small numbers or can be shed by adult cattle that can carry the lungworm over winter. This means that in favourable conditions like the last two months, we will see a huge increase of infective lungworm larvae on pasture. What is frustrating is that this can occur quite rapidly.
Ideally, young cattle will develop immunity to lungworm due to low levels of exposure over time. Where we see issues is when young cattle have been over dosed and not allowed develop this immunity or when there are large burdens the cattle cannot mount an immune response. So grazing management can play a huge role in the spread of the parasite in young stock.
The clinical signs to watch out for are:
- 1. Coughing intermittently when grazing. It tends to be a deep harsh lung cough.
- 2. Coughing again when being moved or disturbed.
- 3. Some animals will have more rapid breathing and often, in severe cases, will have the mouth open and tongue out.
- 4. With milking cows, you may see a drop in milk yield.
- 5. Cattle with lungworm are much more likely to pick up viral infections.Adult cows can pick up infection also and this is what we are seeing in a lot of dairy herds at present. This can occur due to poor immunity being developed through low exposure at a young age or being dosed heavily in first two grazing seasons.
The second more complicated reason is reinfection syndrome where animals come across a large challenge and the immune response is unable to cope with lungworm. What happens is that there are two types of immunity; one in the gut and the second in the lungs. It is thought the gut immunity only lasts six months, allowing larvae to get to the lungs in older cattle. The immunity in the lungs lasts much longer however, and when these larvae get to the lungs they can cause a huge reaction. This will lead to a lot of coughing in adult cows and can be difficult to diagnose.
To diagnose lungworm, you can often go on clinical signs or in younger animals faecal tests to detect larvae. In adult cows it can be more difficult as faecal tests are unreliable. What we now do is a blood test on the cows to check for antibodies to measure exposure and antibody levels. Unfortunately, this is an expensive test.
So with lungworm we need to be extremely vigilant and control the parasite through understanding risk at farm level.
When controlling
- 1. Grazing management can help but, regardless of this, with the right conditions you can still see issues. Repeat grazing for young stock on the same ground each spring is a bad idea.
- 2. Choosing when you dose and with what is very much based on individual farms risks. There are no resistance issues. I personally prefer white or yellow doses as ivermectin clear drenches don’t allow immunity to develop adequately when over used.
- 3. It is important to remember that, with a lungworm problem, when using ivermectins you can make the problem worse because they are so effective at killing the worm you can often get a worsening of coughing or symptoms after dosing. What happens is the dead worms will cause a reaction in the lungs.
- 4. Vaccination with a product called huskvac is something more farms will have to consider in the future.The main aim of this article is not to cause fear but to encourage farmers to remain vigilant and be aware we are in a risk period for lungworm. Your own vet is best placed to advise on treatments and formulate control plans for you.
(Source – Irish Farmers Journal – Tommy Heffernan – 30/09/2015)